When you create two or more AP-manager interfaces, each one is mapped to a different port.
Before an access point joins a controller, it sends out a discovery request. From the discovery response that it receives, the access point can tell the number of AP-manager interfaces on the controller and the number of access points on each AP-manager interface. The access point generally joins the AP-manager with the least number of access points. In this way, the access point load is dynamically distributed across the multiple access point manager interfaces.
Access points may not be distributed completely evenly across all of the AP-manager interfaces, but a certain level of load balancing occurs.
For CAPWAP, the controller needs one management interface for all controller-controller communications. AP-manager interfaces manages the communications from controller to access points. The access points join the controller using the IP address of the AP manager. The IP address of the AP manager is used as the tunnel source for the CAPWAP packets from the controller to the access points and the destination source for the CAPWAP packets from the access points to the controller. The AP manager is a Layer3 interface that maps to an SVI in Cisco IOS software.
You can configure the AP-manager and management interface in any order, however; we recommend that you configure the management interface before configuring an AP-manager interface.
Mapping of an AP-manager interface to an SVI that does not have a mapped VLAN is valid, however; you must map the AP-manager interface to an SVI that contains a mapped VLAN. The controller assumes that the mapping of an SVI to an existing VLAN; in the absence of which the SVI status would be operationally down indicating that no access points join the controller.